This invention relates to doors, of the kind as used in underground tunnels and passageways for the control of ventilation.
Traditionally, the door apparatus is provided as a pair of door-sections, which are hinged one to the left side-wall and the other to the right side-wall of the passage. The door-sections operate like canal-lock gates, i.e the door-sections extend each halfway across the passage to close off the passage to airflow, and the door-sections open both together, to lie flat against the sidewalls of the tunnel, to allow traffic to pass through.
When the doors are being opened or closed, the traditional design requires the door-sections to open either both against, or both with, the flow of air passing through the passage. Mine ventilation doors can be large, for example each door-section may be three meters high and three meters wide. Even a small pressure difference across the doors creates an enormous force tending to blow the doors open, or closed, and the door actuation system must provide enough force to overcome the pressure differential.
Providing a means, down a mine, for exerting such large forces is not only inconvenient, but can lead to safety problems. It is not unusual for mine-workers to be injured by ventilation doors. In order to close the doors against the air pressure, the actuators have to be so powerful they cannot even detect the presence of the worker. Precautions must be taken to prevent the door-sections being blown open or closed, in case the power supply to the actuator should fail.
One proposal has been to provide two pairs of door-sections, arranged in an air-lock configuration. The force needed to open or close one pair of door-sections of course is much less if the passage is already closed by the other pair of door-sections. However, the ventilation fans are usually not switched off simply to enable the passage is to be changed from being open for ventilation to being closed (or vice versa); since the ventilation status of the passage still has to be changed while the fans are on, one of the door-section pairs has to open or close against the full airflow. Arranging mine doors in an air-lock configuration, besides doubling the cost, in fact does not allow the designer to provide a less powerful actuation system.
The invention provides a door apparatus in which the door-sections open, not in the manner of lock-gates, but in the manner whereby one door-section opens upstream while the other door-section opens downstream. Thus, one door-section opens against, while the other opens with, the air pressure. Thus, one door-section is being urged to blow open, while the other door-section is being urged to blow closed.
In the invention, the door apparatus includes a mechanical linkage, which couples and connects the door-sections, and transfers forces between the door-sections. Theoretically, the door-sections can be exactly balanced: i.e the force tending to blow the upstream door-section closed is exactly balanced by the force tending to blow the downstream door-section open. That being so, the force required to actuate the door apparatus from the open condition to the closed condition (and vice versa) is minimal. Because the force required from the actuator is so small, the power of the actuator now can be light enough not to cause injury to a worker who might have fallen between the door-sections.
The actuation force is, at least theoretically, independent of the magnitude of the air pressure differential acting on the door. In practice, a large pressure differential puts larger forces onto the door hinges and the linkage, and the increased friction would be reflected in an increase in the force needed to open and close the door.
Since the actuator only need provide a small force, the actuator can be a wholly electrical unit. This is preferred because, increasingly, below-ground operations must have the ability to be powered and controlled remotely from the surface, and electrical devices are much more convenient than pneumatic or hydraulic force-actuators in this regard. With traditional pneumatically-operated doors, often the door-actuators are the only below-ground machines that require compressed-air lines to be run down from the surface. Also, an all-electric actuator can be powered by stand-by batteries in emergencies.
For vehicular traffic, the actuator should be provided with a signal sensor, enabling the driver to remain with the vehicle while operating the doors. But, as mentioned, by the use of the invention, the door-sections can be balanced sufficiently that the worker can pull the door-sections open by hand, walk through the gap, then close the door-sections, again by hand. The worker might be discomforted by the wind draft that then blows through the gap, but at least the worker can, if required, control the opening and closing of the doors by hand action, even in the event of power failure. Preferably, the actuator should be of the type that permits the door-sections to be moved when the actuator is not being supplied with power, whereby the worker does not have to dismantle the actuator in order to open and close the doors by hand.
With the invention, there is no need for the traditional small man-door to be let into the ventilation-door. Indeed, traditional man-doors have been subject to slamming or blowing open, violently enough to cause injury to an unwary worker. However, a man-door may be provided, if desired. In fact, one field for applying the invention is to replace the (dangerous) man-doors in existing traditional ventilation-doors by a pair of half-doors which are operated in the force-balanced, one-upstream-one-downstream, manner of the invention.
The invention provides a manner of operating mine ventilation-doors which, though safer and more convenient, can be significantly less expensive than traditional systems. As will be described, the linkage connecting the door-sections can be cheap to manufacture, and need not require sophisticated set-up and adjustment.